The present invention relates to a method for producing boehmite particles which can be used as a raw material for the production of alumina particles, and a method for producing alumina particles.
Alumina particles are used, for instance, as abrasive grains in an application of polishing an object to be polished, such as a semiconductor device substrate, a substrate for a display, a hard disk substrate, and a sapphire substrate for an LED. In order to obtain a polished surface with high smoothness and few defects, the particle size of the alumina particles to be used as abrasive grains is preferably as small as possible. A polishing composition which contains alumina particles as free abrasive grains generally has a higher removal rate (polishing rate) against the object to be polished than a polishing composition which contains colloidal silica as free abrasive grains. However, even in the case of a polishing composition containing alumina particles, the removal rate by the polishing composition against the object to be polished is not particularly high when the alumina particles have relatively small particle sizes. In addition, when the alumina particles have relatively small particle sizes, it is difficult to remove the alumina particles that have deposited on the polished surface (in other words, ease of washing off the alumina particles on the polished surface is not high).
As is described in Japanese Laid-Open Patent Publication No. 3-277683 and Japanese Laid-Open Patent Publication No. 5-271647, it is known to use alumina particles including primary particles each having an angular shape as abrasive grains. Alumina particles including primary particles each having a hexahedral shape, which are conceptually included in the angular alumina particles, are capable of polishing an object to be polished with a high removal rate and are easily washed from the surface of the object after polishing even when their particle sizes are relatively small. Accordingly, such alumina particles are suitable as abrasive grains in an application of polishing an object to be polished so as to obtain a polished surface with high smoothness and few defects.